252 MILK HYGIENE 



3. Add ten drops of commercial rennet extract and 

 mix thoroughly with the milk to quickly coagulate. 



4. After coagulation cut curd fine with case knife to 

 facilitate separation of whey; leave curd in whey one- 

 half hour to an hour ; then drain off whey at frequent 

 intervals until curd is well matted. 



5. Incubate curd at 98° to 102° F. by immersing jar 

 in warm water. Keep jars covered to retain odors. 



6. After six to nine hours' incubation open jars and 

 observe odor ; examine curds by cutting same with sharp 

 knife and observe texture as to presence of pin holes or 

 gas holes. Observe odor. 



7. Very bad milks will betray the presence of gas- 

 producing bacteria by the spongy texture of the curd 

 and will have an off flavor. 



8. If more than one sample is tested at the same 

 time, dip knife and thermometer in hot water before 

 each time used. 



Milks showing the presence of gas or bad odors in 

 any considerable degree are milks that have been more 

 or less polluted with extraneous organisms or carelessly 

 handled, and as a consequence such milks show a curd 

 filled with small pin holes due to gas. It is not intended 

 that this test should be used for absolute indication of 

 the presence of gas-producing organisms, but rather it 

 has been of service in the detection of the condition of 

 market milk. 



Other methods of detecting gas-producing organisms 

 in milk. Gas-producing organisms in milk may be 

 tested for, as in water, with glucose or lactose broth in 

 fermentation tubes. Tests similar to presumptive tests 

 for B. coli in water analysis may be made by inoculating 

 into these broth fermentation tubes a c.c. each of the 

 1-100, 1-1,000 and 1-10,000 dilutions, or if B. coli or- 

 ganisms are to be numerically determined the milk may 

 be plated in lactose litmus agar, red colonies counted 

 and species tests worked out. Lactose-bile medium has 

 also been used for the determination of B. coli in milk. 



The presence of these gas-producing organisms in 

 abundance usually indicates dirty condition of stables, 

 cows or vessels. In small quantities they may be found 

 in most milks. 



